Method, apparatus, and tools for precision polishing of lenses and lens molds

ABSTRACT

A tool, apparatus, and method for polishing objects having a wide variety of materials and shapes including precision optical surfaces, injection mold inserts, and thin film coating dies; and in particular, objects having deeply concave precision surfaces. The tool has a rotatably drive wheel engaged with a polishing wheel by use of a polishing foil formed as a flexible belt. The polishing wheel may have a cavity within, such cavity being inflatable using a variety of fluids having a range of physical properties. The polishing wheel is adjustably positionable against an object to be polished by actuating means joined thereto. The apparatus comprises a multi-axis computer controlled machine to which the tool is attached.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0001] This application is a continuation-in-part of copending patent application U.S. Ser. No. 10/439,833, filed on May 16, 2003.

FIELD OF THE INVENTION

[0002] A method and apparatus for correcting surface errors, and for polishing objects comprising a wide variety of materials and shapes including precision optical surfaces and injection mold inserts, particularly those objects having deeply concave precision surfaces.

BACKGROUND OF THE INVENTION

[0003] This invention relates to a method and apparatus for correcting figure errors, and for polishing a wide variety of materials and shapes including but not limited to precision optical surfaces, injection mold inserts, thin film coating dies, and the like. The method of the present invention provides for improving and further finishing of any surface, ranging from a relatively rough ground surface to a polished surface.

[0004] Typically the part being finished according to the present invention is measured with a coordinate measurement machine (CMM), a surface profilometer, an interferometer, microscope or some other measuring instrument capable of giving surface roughness and or profile data. The data from such measurement and analysis is then entered into a machine process-controlling computer that then manipulates the data into process parameters for improving or polishing the desired component by a polishing machine of the present invention. One or more iterations of the process of the present invention may be required to achieve the desired results. In the preferred embodiment, a polishing tool comprising an inflatable bladder is attached to and driven by the tool spindle of the polishing machine. The part to be improved or polished, whether spherical, aspherical or parabolic in shape, is placed into the work piece spindle of the polishing machine. If such part is not axially symmetrical, it may be held in a braked position in the work piece spindle, or held in a fixture on a table of the machine. The polishing tool is then compressed against and traversed in a path over the component. Several variables are able to be controlled as process parameters, so that the desired finishing results are achieved.

[0005] In another preferred embodiment, the polishing tool further comprises actuation means to extend and/or position and/or compress the inflatable bladder or other compliant part with respect to the part to be improved or polished. Such actuation means may comprise one or more linear actuating devices such as e.g. , air operated or hydraulically operated cylinders.

[0006] The present invention provides a method and apparatus for which the main goal is to polish out and remove defects left from a preceding grinding operation or to improve the accuracy of a workpiece such as a lens, mirror, insert for an injection mold, or coating die, such accuracy being relative to the intended use of the workpiece; and also to improve the economy of the polishing process.

[0007] In the following specification, for the sake of linguistic simplification, only optical components, also known as precision optics or optics generally, are typically mentioned as the workpiece. However, it is to be understood that all lenses, spherical and aspherical, conformal optics, mirrors, plano shapes, injection mold components, coating dies, and other articles of manufacture that require highly polished accurate surfaces are also included in the description, and are to be considered as being within the scope of the present invention. Materials that may be finished using the method and apparatus of the present invention include, but are not limited to brittle amorphous materials such as e.g., glass, ceramics, infrared materials such as quartz, and the like. Also included are metals such as e.g., tool steel, stainless steel, and the like; crystalline materials such as e.g. silicon; and any other workpieces requiring high finish and form specifications.

[0008] Currently, many optical lenses are made beginning with a “blank” starting part (such blank part being an approximately formed and generally roughly finished piece) in several processing steps. The process steps typically include fine grinding, followed by conventional polishing techniques wherein the surface roughness and surface accuracy of the lens is significantly improved. This prior art process is sufficient for many conventional low-precision lenses, but when the desired lens has a shape that is not spherical or piano and/or where such conventional methodologies cannot be applied e.g., aspherics, or where the lens has very high accuracy requirements, such prior art process is not sufficient. In such circumstances, the method and apparatus of the present invention is advantageous.

[0009] In particular, several prior art procedures are known to the applicants as being used to fabricate precision optics. One of these procedures is known in the art as small spot tool polishing, wherein a pencil like polishing tool (typical 5 to 15 millimeters in diameter) is used, such tool comprising a polishing medium of polyurethane, felt, pitch or some other combination of polishing material bonded thereto, and typically known as a foil.

[0010] In one specific embodiment of the small spot tool polishing process, a polishing tool, rotating around the axis thereof, is mounted to a robotic arm and is traversed by such arm across the lens surface, or alternatively, such tool is built into a computer numerically controlled (CNC) polishing machine. During the process a polishing suspension is applied, while the polishing tool is traversed across the lens surface through a predetermined typically computer controlled path. Depending on the correction geometry required, different volumes of material are abraded, or polished, from the lens surface. The robotic arm of the correction machine is programmed in such a way that the polishing tool is moved with different dwell times at different positions as such tool passes over the lens. Thus, when more material must be removed at a particular location, the dwell time is increased, and vice versa. During the polishing process, the lens may be rotate around its axis, or be it may be fixed in specific positions if the robotic arm of the correction machine has such capability.

[0011] In the small spot procedure there are several disadvantages. The polishing tool wears quickly due to its small diameter, which results in the distinct disadvantages of a) typically very long polishing cycles; and b) because of quicker degradation of the small polishing foil it is much more difficult and costly to develop accurate corrective polishing routines. Another disadvantage is due to the small spot diameter of the tool. Material removal rates are typically very slow, since the performance is directly proportional to the size of the surfaces that are in contact during the polishing routine.

[0012] Another known finishing/polishing procedure is known as magnetorheological finishing (MRF). With the use of the MRF process, marked improvements in surface roughness and accuracy can be achieved. In general, the MRF process produces better results than small spot polishing. Reference may be had e.g., to U.S. Pat. Nos. 5,795,212, 6,106,380 (deterministic magnetorheological finishing), 5,839,944 (apparatus deterministic magneto-rheological finishing), 5,971,835 (system for abrasive jet shaping and polishing of a surface using a magnetorheological fluid), 5,951,369, 6,506,102 (system for magnetorheological finishing of substrates), and 6,267,651 and 6,309,285 (magnetic wiper). The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.

[0013] With the MRF procedure a polishing suspension is used, which contains particles that can be magnetized and therefore under the effect of strong electromagnets can be solidified. A polishing suspension is applied sequentially on the outside surface of a cylinder rotating around its horizontal axis. The polishing suspension is disposed in a thin band upon the outside surface of a rotating cylinder, and is conveyed to a location where a strong magnetic field is focused. This field is created by magnets surrounding both sides of the wheel. Under the influence of the magnetic field, the polishing suspension increases in viscosity until it is substantially an abrasive solid, thereby forming a stiff polishing body, which becomes the polishing tool. Thus within this area i.e., in the upper apex of the polishing tool, a lens may be polished by such solidified MRF fluid. As the wheel rotates the polishing suspension leaves the contact area of the lens and the magnetic field, and is then vacuumed/wiped off of the wheel and continuously recirculated.

[0014] During the MRF polishing process, the lens rotates. The lens carrier with the lens can be placed by means of a tilting device and an assigned axis control at angles to the vertical axis. With a large angle of inclination, the edge of the lens touches the polishing tool, while with a small angle of inclination the center of the lens comes into contact with the polishing tool. Additionally the lens carrier is guided in such a way that it also can execute vertical movements. With a rotating lens, the angles of inclination are continually varied; such variation is accomplished with the use of virtual pivot point computer controlled motion that combines the two linear and one rotary axes and thus keeps the lens in consistent contact with the polishing tool. A spiral develops on the lens that is the trajectory of the point of contact between the solidified polishing suspension and the lens surface.

[0015] The different material removals necessary for the correction of the lens geometry are implemented as follows: The dwell time of the point of contact on a certain area on the lens surface can be varied by appropriately controlling the courses of motion. Since the material removal is proportional to the dwell time, the desired corrections can be achieved. The polishing suspension in its “firmness” can be influenced by variation of the magnetic field strength. This further enables different material removal rates. A further correction option results by varying the depth of submergence of the lens into the polishing suspension.

[0016] Although the MRF process has many attributes, such process also has some distinct disadvantages as follows: 1) Cost-effective polishing of deviations is limited to errors of less than 200 nanometers only. This is a result of the lack of “stiffness” of the magnetically stiffened polishing suspension and the ability to shear/polish features greater in magnitude. 2) There is a very high capital cost of entry into the MRF technology. The process entails very complex technology, which also increases the cost of operation. It is also necessary to continuously change the MRF polishing suspension, which is very expensive because of its proprietary nature. 3) Parts made of magnetic materials are not able to be polished with this process, as the workpiece will become magnetized and not release the magnetic process fluid. 4) Small concave parts cannot be polished due to the configuration and size of the MRF polishing wheel.

[0017] Reference may be had to German patent DE0031057 of R. Mandler, the disclosure of which is incorporated herein by reference. There is disclosed in such patent a method for polishing of lenses and mirrors for high resolution optics. The lens/mirror is polished conventionally and measured by interferometric means to map the surface and to determine how much material needs to be removed and from where. The lens is supported on a rotating holder with two degrees of movement, while the polishing wheel is supported with axial adjustment. The polishing wheel has a flexible rim inflated with a variable internal pressure to adjust the hardness of flexible rim/tire. Mandler relies upon changes in pressure on a polyurethane foil to impact removal rates and finishing qualities. Although as stated therein, the apparatus of Mandler can change the pressure during the process, such process does not have the ability to change to softer media, such as felt or other softer synthetic materials as is disclosed and claimed in this application. Mandler also discloses only a 3-axis process, whereas embodiments of the present invention include control and operation with respect to five or more axes.

[0018] With the method and apparatus of the present invention, many of the disadvantages of the aforementioned techniques are non-existent, or rendered insignificant. It is therefore an object of this invention to provide an apparatus for precision polishing of objects comprising a wide variety of materials and shapes.

[0019] It is a further object of this invention to provide a versatile and adjustable tool for precision polishing of objects comprising a wide variety of materials and shapes.

[0020] It is another object of this invention to provide a method for precision polishing of objects comprising a wide variety of materials and shapes.

[0021] It is an object of this invention to provide a method and apparatus for precision polishing of objects that is simple and has a low operating cost.

[0022] It is an object of this invention to provide a method, a tool, and an apparatus that in having the ability to remove low, mid, and high spatial surface errors, reduces the requirements of the pre-fine grind tolerances, which in turn reduces the requirements of the fine grinding apparatus.

[0023] It is an object of this invention to provide a method and apparatus for precision polishing of objects that has a high rate of material removal.

[0024] It is an object of this invention to provide a tool for precision polishing of objects that has high longevity and stability of operation.

[0025] It is an object of this invention to provide a method, a tool, and an apparatus that has the ability to perform polishing of object surfaces that are deeply concave in shape.

SUMMARY OF THE INVENTION

[0026] In accordance with the present invention, there is provided a polishing tool comprising a base for affixing objects thereto; a drive wheel joined to a rotatable shaft, said drive wheel having a perimeter, and said rotatable shaft disposed in a housing joined to said base; a rotatable polishing wheel having a perimeter; a polishing foil engagable with a portion of said perimeter of said drive wheel and engagable with a portion of said perimeter of said polishing wheel and a first actuating means for engaging said polishing foil with said portion of said perimeter of said drive wheel and with said portion of said perimeter of said polishing wheel.

[0027] In accordance with the present invention, there is provided a polishing tool comprising a base for affixing objects thereto; a drive wheel joined to a rotatable shaft, said drive wheel having a perimeter, and said rotatable shaft disposed in a housing joined to said base; a rotatable polishing wheel having a perimeter; a polishing foil engagable with a portion of said perimeter of said drive wheel and engagable with a portion of said perimeter of said polishing wheel and a first actuating means for for positioning said polishing wheel and said polishing foil.

[0028] In accordance with the present invention, there is provided an apparatus for polishing objects comprising a first linear slide movable along a first axis, disposed upon a base; a first rotatable spindle engaged with said first linear slide, said first rotatable spindle further comprising a first chuck, and said first rotatable spindle aligned with said first axis; a second linear slide movable along a second axis, engaged with said first linear slide, with said second axis disposed orthogonally to said first axis; a second rotatable spindle engaged with said second linear slide, said second rotatable spindle further comprising a second chuck; and a polishing tool engaged with said second chuck of said second rotatable spindle, said polishing tool comprising a base for affixing objects thereto; a drive wheel joined to a rotatable shaft, said drive wheel having a perimeter, and said rotatable shaft disposed in a housing joined to said base; a rotatable polishing wheel having a perimeter; a polishing foil engagable with a portion of said perimeter of said drive wheel and engagable with a portion of said perimeter of said polishing wheel and a first actuating means for engaging said polishing foil with said portion of said perimeter of said drive wheel and with said portion of said perimeter of said polishing wheel.

[0029] In accordance with the present invention, there is provided a method of polishing a surface of an object using a machine tool apparatus comprising a polishing tool comprised of a base for affixing objects thereto; a drive wheel joined to a rotatable shaft, said drive wheel having a perimeter, and said rotatable shaft disposed in a housing joined to said base; a rotatable polishing wheel having a perimeter; a polishing foil engagable with a portion of said perimeter of said drive wheel and engagable with a portion of said perimeter of said polishing wheel, said polishing foil rotatably coupling said drive wheel with said polishing wheel; and a first actuating means for engaging said polishing foil with said portion of said perimeter of said drive wheel and with said portion of said perimeter of said polishing wheel; said method comprising the steps of preparing said polishing tool for said polishing of objects; preparing and programming said machine tool for said polishing of objects; executing a first polishing cycle with said machine tool apparatus, wherein said polishing tool is in contact with said surface of said object; and measuring said surface of said object.

[0030] The method and apparatus of the present invention is advantageous because it is simple and lower in cost compared to other approaches, and it can be adapted for the polishing of a variety of materials and shapes, particularly those objects having deeply concave shapes. As a result of the invention, articles of manufacture such as precision optics, injection mold inserts, and thin film coating dies can be polished with high precision at a high throughput and low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The invention will be described by reference to the following drawings, in which like numerals refer to like elements, and in which:

[0032]FIG. 1 is a schematic representation of one preferred polishing apparatus of the present invention;

[0033]FIG. 2A is a cross-sectional view of one preferred polishing tool of the present invention;

[0034]FIG. 2B is a side elevation view of the polishing tool of FIG. 2A, in the process of polishing a convex lens;

[0035]FIG. 3 is a cross-sectional view of another preferred embodiment of a polishing ring disposed upon the polishing tool of FIG. 2A;

[0036]FIG. 4 is a cross-sectional view of one preferred embodiment of a polishing ring disposed upon the polishing tool of FIG. 2A;

[0037]FIG. 5 is a flowchart depicting a method of assembly of the preferred polishing tool of FIG. 2A;

[0038]FIG. 6 is a flowchart depicting a method of preparing the preferred apparatus of FIG. 1 for a polishing operation; and

[0039]FIG. 7 is a flowchart of a complete method of polishing an optic using the apparatus and polishing tool of the present invention.

[0040]FIG. 8A is a cross-sectional view of another preferred polishing tool of the present invention;

[0041]FIG. 8B is a side elevation view of the polishing tool of FIG. 8A, in the process of polishing a concave lens;

[0042]FIG. 9 is a schematic representation of another preferred polishing apparatus for polishing concave spheres, aspheres, convex spheres, or other conformal shapes;

[0043]FIG. 10 is a first perspective view of another preferred polishing tool of the present invention comprising single cylinder actuation means to extend and/or position the inflatable bladder or other compliant part with respect to the part to be improved or polished;

[0044]FIG. 11 is a side elevation view of the polishing tool of FIG. 10;

[0045]FIG. 12 is a top view of the polishing tool of FIG. 10;

[0046]FIG. 13 is a second perspective view of the polishing tool of FIG. 10, taken from the plate side of the polishing tool;

[0047]FIG. 14 is a first perspective view of another preferred polishing tool of the present invention comprising twin cylinder actuation means to extend and/or position the inflatable bladder or other compliant part with respect to the part to be improved or polished;

[0048]FIG. 15 is a side elevation view of the polishing tool of FIG. 14;

[0049]FIG. 16 is a top view of the polishing tool of FIG. 14;

[0050]FIG. 17 is a second perspective view of the polishing tool of FIG. 14, taken from the plate side of the polishing tool;

[0051]FIG. 18A is a cross-sectional elevation view of the polishing tool of FIG. 14, shown disengaged with a deeply concave object to be polished;

[0052]FIG. 18B is a cross-sectional elevation view of the polishing tool of FIG. 14, shown engaged from a deeply concave object to be polished;

[0053]FIG. 19 is a perspective view of a first preferred polishing apparatus of the present invention comprising a polishing tool having actuation means to extend and/or position the inflatable bladder or other compliant part with respect to the part to be improved or polished;

[0054]FIG. 20 is a perspective view of a second preferred polishing apparatus of the present invention comprising a polishing tool having actuation means to extend and/or position the inflatable bladder or other compliant part with respect to the part to be improved or polished;

[0055]FIG. 21 is a perspective view of a third preferred polishing apparatus of the present invention comprising a polishing tool having actuation means to extend and/or position the inflatable bladder or other compliant part with respect to the part to be improved or polished; and

[0056]FIG. 22A and FIG. 22B are schematic representations of means for engaging a polishing foil of the polishing tools of FIGS. 10-13 and FIGS. 14-18B.

[0057] The present invention will be described in connection with certain preferred embodiments, however, it will be understood that there is no intent to limit the invention to the embodiments described. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] For a general understanding of the present invention, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate identical elements. In describing the present invention, the following term(s) have been used in the description:

[0059] As used herein, the term figure error (or form error) is the measured global deviation from the desired surface shape e.g., a sphere, asphere or polynomial geometric shape.

[0060] As used herein, form error is a low frequency error. Traditionally in optics, irregularity and power are the two specifications that need to be considered. Irregularity is the deviation from a perfect surface. Power is the resulting average surface dimensions e.g., radius of curvature.

[0061] As used herein, the term zonal enhancement is meant to indicate a correction of the figure error, which is located symmetrically or asymmetrically at one specific location (zone) on the work piece. For example, if a cylindrical disc was the workpiece, a zonal error would be in one sector of the disc, or in a specific band or ring on the disc, or other rotationally symmetrical part.

[0062] As used herein, the terms spot, high, mid- and low spatial frequencies in reference to errors in a surface to be polished are meant to indicate the following. Low spatial frequencies are errors that appear only once to a few times across a particular surface. Mid-spatial frequencies are errors that occur many times across a surface of a part, generally have a periodic spacing of between 80 microns and 3 mm, and are typically caused by cutter marks due to machine or tool vibrations. High spatial frequencies are errors that happen on a microscopic scale, which may appear thousands of times across the surface of a part, and have a periodic spacing of less than 80 microns.

[0063] As used herein, the term polishing, when used in reference to a workpiece to be finished, is meant to indicate a chemo/mechanical process that ablates material from a surface.

[0064] As used herein, the term correction of form, or form error modification correction, when used in reference to a workpiece to be finished, is meant to indicate the same as has been defined for figure error.

[0065] As used herein, the term figure, when used in reference to a workpiece to be finished, is meant to indicate polishing in a correction for error in the figure and or form, which are the same.

[0066] As used herein, the term surface roughness, when used in reference to a workpiece to be finished, is meant to indicate high frequency errors, which are typically the result of brittle fracture regime (e.g.microcracks).

[0067]FIG. 1 is a schematic representation of one preferred polishing apparatus of the present invention. Referring to FIG. 1, polishing apparatus 100 is configured for polishing convex spheres, aspheres, shallow concave spheres, or other conformal shapes. Polishing apparatus 100 comprises a base 102 that supports Y-axis linear slide 104, the motion of which is bi-directional along Y-axis 105 (directed perpendicular to the plane of FIG. 1). Linear slide 106, the motion of which is bi-directional along X-axis 107, is mounted upon Y-axis linear slide 104. These linear slides 104 and 106 are both computer numerically controlled (CNC) positioning devices, providing programmable motion in the X-Y plane.

[0068] Workpiece spindle 108 is mounted upon linear slide 106, such that the motion of spindle 108 is bidirectionally programmable along axis 109, which is parallel to X-axis 107. Thus spindle 108 is movable by computer control along axis 109, depending on the requirements or the polishing process. Rotatable workpiece chucking device 110 is attached to end of workpiece spindle 108. The workpiece 10 to be polished is engaged and held by chuck 110 and rotated by spindle 108 around the central rotary axis thereof.

[0069] Apparatus 100 further comprises vertical slide 120 attached to polishing machine column 122, which is joined to base 102. The motion of vertical slide 120 is bi-directional along Z-axis 121. Polishing tool spindle 124 is attached to the Z-axis slide 120. The rotational speed (RPM) of this spindle is varied by the computer depending on the desired removal rate of material from workpiece 10. Apparatus 100 further comprises a rotatable chucking device 126 attached to the end of polishing tool spindle 124, in which polishing tool 128 of the present invention is inserted and rotated. Polishing tool 128 is provided in a variety of shapes, sizes, and materials (e.g. see polishing tool 200 of FIG. 2A and 2B), as will be described subsequently in this specification.

[0070] In summary, there are three linear and one rotary axis drives in this configuration, all of which are computer controlled to allow for a deterministic polishing process, to be described subsequently in more detail in this specification.

[0071] Referring again to FIG. 1, in the preferred embodiment, apparatus 100 further comprises a fluid delivery system 130 for delivery of a homogeneous liquid or a liquid slurry. In some embodiments, delivery system 130 delivers a liquid containing finely divided solid particles, and as such is considered a slurry, a suspension, or a particulate dispersion. Such particles are preferably abrasive polishing particles with a hardness sufficient to wear a typical optical material such as e.g. glass. Such particles may comprise e.g., silica, alumina, ceria, diamond, and the like, and mixtures thereof. Many other hard, abrasive particulate materials such as e.g., carbides, nitrides, etc. will be apparent to those skilled in the art.

[0072] In other embodiments, delivery system 130 delivers a homogeneous liquid substantially free of solid particles. Suitable liquids may be e.g. water, water soluble oils or lubricants (such as e.g. glycerine), hydrocarbon oils, silicone oils, and the like. The selection of a particular homogeneous liquid or a particulate slurry will depend upon the particular optical part being polished, and upon the desired end results.

[0073] Referring again to FIG. 1, slurry or fluid delivery system 130 comprises a reservoir (not shown), a slurry/fluid mixer 132, and a slurry/fluid pump 134. Slurry/fluid delivery system 130 is used to supply an abrasive slurry/fluid (not shown), which is delivered through conduit 136 and directed by nozzle 138 upon the polishing tool 128 and workpiece 10, at the area of contact there between.

[0074]FIG. 2A is a cross-sectional view of one preferred polishing tool of the present invention used in apparatus 100 of FIG. 1, according to the methods of the present invention. Referring to FIG. 2A, polishing tool 200 comprises a main body or bladder mandrel 202 having a shank 201 at a proximal end 224 thereof, and a flange 211 at a distal end thereof, around which a bladder 204 is disposed and sealably engaged therewith. Compression washers 206 and 207 are disposed on both sides of bladder 204, and are held in place by locking nuts 208 and 209, respectively. Nuts 208 and 209 and washers 206 and 207 provide sealing means in that nuts 208 and 209 and washers 206 and 207 hold bladder 204 tightly against flange 211 of mandrel 202. In the preferred embodiment, lips 246 and 248 of bladder 204 are disposed and held firmly in grooves 242 and 244 of mandrel 202, so that bladder 204 is sealed to mandrel 202.

[0075] End 210 of mandrel 202 has an axial bore 212 disposed therein, which is connected to at least one radial bore 214, or preferably a plurality of radial bores 214 extending to a cavity 216 disposed in the perimeter 218 of mandrel 202. Such axial bore 212 and radial bores 214 form a continuous passageway such that cavity 216 is in communication with the atmosphere outside of tool 200. Thus axial bore 212 and radial bores 214 allow the cavity 216 to be filled and pressurized with a fluid delivered through inflation device 220, which is disposed and sealed in axial bore 212 at the end 210 of mandrel 202.

[0076] Polishing tool 200 further comprises a ring assembly 230 of polishing material disposed around the outer perimeter of bladder 204. FIG. 3 is a cross-sectional view of one preferred embodiment of a polishing ring disposed upon the polishing tool of FIG. 2A. Referring to FIG. 3, ring assembly 230 is a dual ring assembly comprising a backer ring 232 of material, over which is disposed abrasive ring 234 comprised of a polishing medium adhered thereto. The resulting polishing ring assembly 230 is disposed around the perimeter of and contiguous with bladder 204. In one preferred embodiment, backer ring 232 consists essentially of a band of poly(ethylene terephthalate) having a thickness of between about 50 microns and about 1000 microns, and a width of between about 2 millimeters and about 30 millimeters.

[0077] Abrasive ring 234 is made of a material of sufficient structural strength to withstand the high shear and tensile forces during polishing, and to resist degradation through exposure to the polishing/lubricating fluid, such as e.g. polyurethanes of various durometers; and various types of felt, cork, and metal and/or resin bond diamond, alumina, and/or zirconium, with a multitude of different types of backings and patterns therein. Abrasive ring 234 preferably has a thickness of between about 1 millimeter and about 5 millimeters, and a width of between about 2 millimeters and about 30 millimeters.

[0078]FIG. 4 is a cross-sectional view of another preferred embodiment of a polishing ring disposed upon the polishing tool of FIG. 2A. Referring to FIG. 4, ring 230 simply comprises a single ring 236 of polishing material disposed around the perimeter of bladder 204. The embodiment of FIG. 4 is used when ring 236 is of sufficient structural strength so as to be able to perform the particular polishing process without the use of a supporting ring disposed contiguously with such ring, as was depicted in FIG. 3. In one preferred embodiment, single ring 236 consists essentially of polyurethane, and has a thickness of between about 1 millimeter and about 5 millimeters, and a width of between about 2 millimeters and about 30 millimeters.

[0079]FIG. 2B is a side elevation view of the polishing tool of FIG. 2A, in the process of polishing a convex lens. Referring to FIGS. 2A and 2B, polishing ring assembly 230 (also known as the foil) is disposed around the outer perimeter of bladder 204 and held in place while bladder 204 is pressurized with a fluid. In operation, polishing tool 200 comprising polishing ring assembly 230 is rotated and engaged with lens 10 such that polishing ring assembly 230 provides a shearing and polishing action upon the surface of lens 10. It will be apparent that the pressure that is applied to bladder 204 will determine the curvature and firmness of the outer surface of polishing ring assembly 230 during a polishing operation.

[0080] Referring again to FIG. 2A, and in one preferred embodiment, bladder 204 has a shape and cross sectional profile that is substantially similar to that of a tire. Bladder 204 is preferably made of a compliant, flexible elastic material that is wrapped or attached at its periphery to the perimeter 218 of mandrel 202. Suitable materials for bladder 204 are e.g., natural or synthetic rubber, silicone, or polyurethane, with a wall thickness of approximately 1 millimeter.

[0081] The tire-shaped bladder 204 may have a variety of specific cross sectional shapes. Before inflating bladder 204 with either air or some other fluid, polishing foil 203 is disposed around or applied to the bladder tool to act as the polishing medium. In one further embodiment, polishing foil 230 is made of polyurethane, and the abrasive polishing medium is provided in a liquid slurry that is pumped onto workpiece 10 and polishing foil 230, as described previously. Alternatively, abrasive particles may be embedded in the polishing foil. Suitable abrasive particles include particles made by the Rhodes Corporation, or by the Minnesota Mining and Manufacturing Company (3M). or it may actually be a product that has In a further embodiment, abrasive particles in the shape of miniature pyramids of polishing medium such as e.g., alumina in varying grit sizes is used. Such products will require that only water be added to wet the polishing medium (the dry powder.)

[0082] In another embodiment, foil 230 comprises a backer ring of poly(ethylene terephthalate) (PET) or similar material to allow softer polishing ring media to be used without tearing or pulling apart, yet maintaining the flexibility required for fine polishing. Bladder 204 of tool 200 is then inflated to a specific pressure depending on the polishing results desired. In such an embodiment, foil 230 is held in position upon bladder 204 by the expansion pressure of the bladder 204 being inflated; thus no adhesive or mechanism is required to bond foil 230 to bladder 204. Such a configuration enables a simple and rapid change of foil polishing media.

[0083] In operation of apparatus 100 of FIG. 1, to which is fitted polishing tool 200 of FIG. 2A, several factors will affect the accuracy and removal rates of the polishing process: the size and shape of bladder 204, the composition of the polishing medium, the composition of the polishing slurry, and the pressure applied to the bladder 204 and also the type of fluid used to inflate the bladder. These latter variables are related to the tool itself (with the exception of slurry composition). Also affecting the accuracy and removal rates of the polishing process included in this invention are variables of the apparatus, such as e.g., example spindle speeds, axis feed rates and polisher path modifications.

[0084] It will be apparent that a variety of fluids may be used to pressurize bladder 204 of polishing tool 200, and that the physical properties of such fluids, as well as the pressure of such fluids also will affect the accuracy and removal rates of the polishing process. The fluid may be selected so as to beneficially affect the polishing process. In one simple and thus preferred embodiment, air is used as the bladder inflation fluid. In another embodiment, a much more dense fluid, i.e. a liquid, such as water is used as the bladder inflation fluid. In such an embodiment, the effective pressure of the outer wall of the bladder is a function of not only the inflation pressure, but also the rotational speed. Such rotational speed provides an additional pressure component due to the centrifugal force exerted by the fluid, in proportion to the square of the rotational speed. Such pressure is analogous to the pressure at the base of a column of liquid acted upon by gravity.

[0085] In a further embodiment, a viscous liquid, such as a hydraulic oil is used as a bladder inflation fluid. The viscosity of such a viscous liquid is preferably between about 10 centipoise and about 100,000 centipoise, and more preferably between about 20 centipoise and about 1000 centipoise. The higher viscosity of such fluid also affects the accuracy and removal rates of the polishing process, because at the contact area of the bladder with the workpiece, the bladder is deformed; hence the fluid disposed within the bladder must undergo viscous flow in this region. Thus a higher viscosity fluid has a greater resistance to deformation, and also being non compressible and thus can provide a beneficial polishing effect. In yet another embodiment, the use of a viscous fluid provides vibration damping to the process, thereby rendering such process more precise, stable, and reliable. In further embodiments, non-Newtonian fluids are used such as e.g. a shear thinning fluid, or a shear thickening fluid. In other embodiments, fluids for which the rheology may be varied by exposure to an electric or magnetic field may be used.

[0086] Referring again to FIG. 2A, in one embodiment, inflation device 220 is a simple, inexpensive check valve. In a preferred embodiment, inflation device is a valve stem, commonly used for the inflation of tubeless tires. In another embodiment, axial bore 212 is sealed, and mandrel 202 of tool 200 is provided with a second axial bore 222 disposed through the opposite end 224 of mandrel 202. In such an embodiment, axial bore 212 is supplied with pressurized fluid from a fluid supply means (not shown) in real time during the polishing process. Such fluid supply means is commonly used as a coolant supply to a machine tool and is well known in the art of machine tools. Thus the pressure within bladder 204 may be varied and/or pulsated during the polishing process, by the delivery or withdrawal of bladder inflation fluid as indicated by arrow 225.

[0087] It is to be understood that many multi-axis CNC machine tools are known in the art, which can be suitably configured to use the polishing tool and the methods of the present invention. The particular configuration of machine tool will depend upon the material properties, size, and shape of the starting blank and the desired finished end product. The present invention is not limited only to the use of the machine tools described herein. For example, such a machine tool could comprise from between two computer controlled axes up to as many as five or six computer controlled linear and/or rotary axes.

[0088] Referring again to FIG. 1, polishing tool 200 and workpiece 10 to be polished are typically inserted into separate spindles 124 and 108 of a multi-axis CNC machine tool. Machine tool apparatus 100 could have a configuration as shown in FIG. 1, or a configuration similar to that of a lathe, mill or some other customized arrangement of the axes, depending upon the part to be polished. Work piece spindle 108 may also be programmed to maintain constant surface speed and also to do zonal enhancements that are especially necessary when there are axial asymmetries in the part. It is to be understood that many different machine variations are possible, and that axes and spindles can be configured in a multitude of combinations/permutations to suit any workpiece shape that needs to be polished. The configuration of the different machine axes and spindles can be in any order as required to enable actuation of the polishing tool over the surface of the workpiece to be polished. Accordingly, all such configurations are to be considered within the scope of the present invention.

[0089] During the polishing operation, the polishing slurry/fluid suspension is fed between the polishing tool 200 and the work piece 10 by slurry delivery system 130. Depending on the results required, the axis traverse feedrates (i.e. the velocities of the linear slides), the workpiece rotational speed in revolutions per minute (RPM) and tool spindle rotational speed in RPM, and the tool path variation in three dimensional space are adjusted via automated computer control.

[0090] In one embodiment, the pressure (and thus the “firmness”) of bladder 204 of polishing tool 200 is preset, and maintained constant during the polishing operation. Depending on the bladder shape, the bladder material properties, the bladder inflation pressure, and the hardness/density of polishing foil 230, a specific pretest is performed in order to characterize the polishing spot profile. As used herein, the term spot profile is meant to indicate the indentation resulting from contacting a test workpiece with polishing tool 200 or 300 by moving the otherwise stationary test workpiece into contact with the polishing tool 200 or 300, thus leaving a depression, indentation, or “footprint” in the part. the test is performed in a standard manner, with the workpiece moved against the tool with a specified displacement for a specified period of time. The resulting volume of the indentation per unit time period it the material removal rate.

[0091] Thus the shape and size of the area produced when the polishing tool is pressed into the test piece for a given period of time is the spot profile. This spot profile is then used in the generation of the time dependent trajectory of the polishing tool over the surface of the workpiece that is required to achieve the desired polishing results. This time dependent trajectory is also known in the art as the tool path and dwell times used in polishing. With the profile characterized, high, mid and low spatial features can be greatly improved through adjustments of the polishing variables, tool rpm, workpiece rpm, axes feedrates, and compression factor. As used herein, the term compression factor is meant to indicate the compressive force applied by the polishing tool against the workpiece, such force being the combination of force due to bladder pressure, and force due to the trajectory of the tool against the workpiece.

[0092] Referring again to FIG. 1, the work piece spindle 108 holds workpiece 10, i.e. the optic or other part to be finished. Work piece spindle 108, and/or polishing spindle 124 as described are attached to computer controlled linear or rotary slides 104, 106, 108, and 120 so that any path or desired motion and dwell times of the polishing tool 200 over the workpiece 10 can be achieved. As described previously, workpiece spindle 108 also acts as a servo controlled positioning axis, the motion of which may be controlled in coordination with the described linear and rotary motions such that any non-axially symmetric irregularities, zonal enhancements, in the workpiece 10 may be also corrected with the polishing method of the present invention. Polishing tool spindle 124 is controlled via a motor and spindle drive (not shown) such that the rotation speed in RPM is variable, and may be adjusted during the polishing process, depending on the process and workpiece requirements.

[0093] As was described previously, there are machine configurations for apparatus 100 that can be provided, depending on the workpiece shape and size, and the desired finished workpiece results. The motions of these axes may be combined so as to not only provide straight, linear, or arcuate motions of the polishing tool 200, but also to provide zigzag, sinusoidal, rotary or other programmable oscillations, in order to achieve the amount of material that is to be removed and to achieve the resulting surface quality.

[0094] Based on the configuration of the machine 100, the spindles and linear and/or rotational slides thereof, and the type/form or the polishing tool(s) to be used, there are various steps required in the process of the present invention, which results not only in the polishing of the workpiece, but also the correction of the surface errors/form of the workpiece.

[0095] In general, the pre-machined (i.e. unfinished) workpiece may be measured with a surface profilometer, an interferometer, a CMM or any other type of measuring device capable of analyzing the geometric shape, in order to quantitatively define the basic starting condition of the workpiece. This information is required to begin the process of improving the components surface roughness, mid-spatial frequency (waviness) and figure. After the analysis, the acquired data on the workpiece is then communicated into the computer control on the machine. This information, along with the software built into the computer control, calculates the process parameters/motion control required giving the desired workpiece improvements.

[0096] The polishing tool spot size and shape is either known based on a library of predetermined empirical parameters obtained experimentally, or it is analyzed through a series of tests. The polishing tool spot size and shape is then sent to the CNC controller. This data is the additional information needed to develop the required polishing tool path motion and speed, and spindle rotational and linear speeds to achieve the desired process results. It is to be understood that the polishing spot size may be affected by the size, shape, material properties, and fill pressure of the bladder, fluid type of the filled bladder, and the polishing foil material properties.

[0097] A more detailed description of methods for using the polishing tools and the apparatus of the present invention will now be described. It is to be understood that the steps in the following descriptions are illustrative of some embodiments of methods, but that the order of the steps described herein may be changed, while still achieving substantially the same end results. Thus, such variations in the methods described herein are to be considered within the scope of the present invention.

[0098] A first preferred step, based upon experience and knowledge of the finishing process and the previously described data obtained on the unfinished part, is to assemble and fit a polishing tool to the polishing apparatus. FIG. 5 is a flowchart depicting a method of assembly of the preferred polishing tool of FIG. 2A in the apparatus of FIG. 1. Referring to FIG. 5, FIG. 1, and FIG. 2A, tool setup process 410 begins with step 412, wherein polishing tool 200 sans polishing ring assembly 230 is fitted in holding chuck 126 of spindle 124. Subsequently in step 414, polishing ring assembly or foil 230 is selected and fitted to bladder 204 of polishing tool 200. Bladder 204 is inflated to hold polishing ring assembly 230 in place thereupon in step 416. A measurement of the center height of polishing ring 230 is made with suitable measuring means such as e.g., a dial indicator, a caliper, a micrometer, and the like in step 418. With steps 412-418 completed, tool setup process 410 is complete. Alternatively or additionally, an alignment fixture may be used to aid in proper position/alignment of the foil and or reinforcement ring

[0099] The overall preparation/setup of the polishing apparatus then follows. FIG. 6 is a flowchart depicting a method of preparing the preferred apparatus of FIG. 1 for a polishing operation. Referring to FIG. 6, and FIG. 1, apparatus or machine setup process 420 begins with step 422, installing the completed polishing tool assembly 200 in chuck 126 of spindle 124. (Step 422 is performed in the event that tool 200 was removed from spindle 124 in order to make the measurement 418 of tool setup process 410 of FIG. 5, or if tool 200 was setup separately from machine 100.)

[0100] Machine setup process 420 continues with step 424, in which the polishing tool dimensional data obtained in measurement step 418 is entered into the CNC process controller of machine 100. The unfinished optic or other workpiece to be polished is then placed into holding chuck 110 of spindle 108 in step 426. The data obtained from measurements made on the unfinished optic that have been described previously are also entered into machine 100 in step 428. In step 430, an analysis of the spot size/removal function of the polisher on the optic is performed, or such data from a previously described library of tool functions is entered into the CNC process controller. In step 432, the CNC process controller is further programmed with polishing tool and polishing medium parametric data such as removal function, polishing spot size, polishing tool medium/material type, polishing tool dimensions/shape, polishing tool bladder pressure, optic/workpiece starting and finished dimensions, and polishing slurry type/composition.

[0101] With all of the relevant data programmed into the CNC process controller, the deterministic path of the polishing tool 200 on the optic 10 is calculated by such controller in step 434. In performing machine setup process 420, depending on the shape and size of the workpiece 10, coordinate offsets will be established in all of the programmable axes 104, 106, 108, and 120, so as to provide the CNC controller of machine 100 the information/location of part 100 such machine 100 will begin the polishing process at the correct location on workpiece 10. At this point, with machine setup 420 complete, some test probing of the workpiece 10 and/or the polishing tool 200 may be implemented to confirm that such starting location is correct. Once the CNC controller of machine 100 has defined/confirmed the “part zero” or starting position of polishing tool 200 upon workpiece 10, the polishing process may begin.

[0102]FIG. 7 is a flowchart of a complete method of polishing an optic using the apparatus and polishing tool of the present invention. Referring to FIG. 7, tool setup process 410, and machine setup process 420 are performed according to the foregoing descriptions of FIG. 5 and FIG. 6. Subsequently, in step 440, the optic polishing cycle is performed, wherein a computer developed path of polishing tool 200 upon workpiece 10 is performed. As described previously, the workpiece spindle 108 and polisher spindle 124 are placed in rotary and linear motion along one or more of axes 105, 107, 109, and 121, depending on the desired results. Note that in some embodiments the part may not be attached to a rotating spindle and may be held in a stationary position, while polishing tool is actuated over the surface thereof.

[0103] In some circumstances, more than one bladder-polishing tool may be required to achieve the desired results in polishing workpiece 10. Accordingly, in one embodiment (not shown), machine 100 is provided with automatic tool changers, to change between multiple polishing tools during the process. In another embodiment (not shown) multiple spindles are provided on machine 100, wherein a first polishing tool on a first spindle performs part of the polishing operation, a second polishing tool on a second spindle performs part of the polishing operation, and so forth, to the extent that multiple tools and spindles are provided on machine 100.

[0104] In the preferred embodiment of polishing cycle 440, but not in all embodiments, at such time when the spindles 108 and 124 have started, but before any motion of tool 200 along axes 105, 107, 109, and 121, there is provided and injection or pumping of a specific polishing slurry or other fluid at the contact location of polishing tool 200 with workpiece 10, which enhances the polishing action or removal rates of material from workpiece 10. As described previously, the path of the polishing tool 200 over the workpiece 10 may include straight, linear, arcuate zigzag, sinusoidal, rotary, spiral, or other programmable motions so as to enhance the removal rate of material from workpiece 10.

[0105] In performing polishing cycle 440 of process 400 of FIG. 7, there are several process parameters that will affect the removal rates and figure enhancement:

[0106] 1. The rotational speed of the workpiece spindle 108 may be controlled to give the effect of constant surface speed of workpiece 10 similar to that of current CNC lathe technology, so as to maintain a constant removal rate of material from the workpiece 10. Such control of spindle speed eliminates the effect of the decreasing or increasing diameter of the contact circle made by the polishing tool 200 upon the rotating workpiece 10, as it will be apparent that the surface speed at the extremity (i.e. maximum diameter) of the rotating workpiece is much greater than the surface speed near the center of the workpiece. As the polishing tool 200 approaches the center of the workpiece 10, the surface speed approaches zero; thus such a variation in surface speed may be compensated for by varying the rotational speed of workpiece spindle 108.

[0107] 2. The speed/position of workpiece 10 may also be controlled so as to improve rotational asymmetries of the workpiece during the polishing cycle 440. For example, if there is an asymmetry that requires more removal in a specific area of workpiece 10, then the part spindle may slow or even stop in this area so as to allow more removal by polishing tool 200. Alternatively, the opposite situation may occur wherein less material removal is required and the workpiece 10 may speed up during polishing in this area to minimize the removal. In other terms, the dwell time of the polishing tool 200 upon the workpiece 10 is adjusted to selectively decrease or remove rotational asymmetries.

[0108] 3. The “stiffness” of the polishing tool may be preset based upon the inflation pressure within the bladder 204 of tool 200. Depending on how “hard” or “soft” bladder 204 is made by inflation pressure, the removal function of tool 200 will be affected. Typically a stiffer polishing tool (i.e. higher inflation pressure) will be used where higher removal functions are required such as in processes where form error modification of workpiece 10 is needed. Likewise, less inflation pressure will be applied to bladder 204 in a final finishing process where the best possible surface finish is required, at the expense of a lower material removal rate. In a further embodiment described previously, inflation pressure may be varied in real time during the polishing cycle 440.

[0109] 4. The compression factor may also be controlled in the polishing cycle 440. Control of the compression factor is achieved through the CNC program wherein the path the polishing tool 200 is moved in a less compressed or more compressed path (“tighter” or “looser path”) over the part, thereby affecting its removal function and rate.

[0110] 5. The tightness of the zigzag or circular motion of the polishing tool 200 in its path over the workpiece 10 may also be adjusted and varied throughout the polishing cycle 440. In one embodiment, the compression factor is held constant while the zigzag or circular motion of the polishing tool 200 is varied. Circular and other motions such as e.g., zigzag, provide better surface finish i.e. polish without leaving artifacts from the tool/abrasive slurry in the surface i.e., grooving.

[0111] 6. The composition, rheological properties, PH, concentration, and flow rate of polishing slurry delivered to the polishing tool/workpiece during the process may be varied to affect removal rates and surface roughness.

[0112] 7. The size, shape, and material properties of the bladder 204 of polishing tool 200 significantly affects the process results and capabilities depending on the workpiece 10 to be polished.

[0113] 8. The material that the bladder is wrapped with (the foil 230) is another variable, which will also affect the material removal and finishing characteristics during polishing cycle 440.

[0114] 9. The physical properties of the fluid medium used to pressurize bladder 204 of tool 200 may be varied. Such physical properties include specific gravity, shear viscosity, and extensional viscosity. Variation of such properties between the basic choice of a liquid or a gas is at least several orders or magnitude. However, there is significant variation between liquids, and there is opportunity for further control based on the use of non-Newtonian liquids, such as shear or extensional thickening liquids, shear or extensional thinning liquids, visco-elastic liquids, and/or magneto-rheological liquids.

[0115] Using variations of the process parameters described in 1-9 above, the removal rates, the surface roughness, mid spatial frequency errors and figure error will be optimized during polishing cycle 440. Upon completion of polishing cycle 440, the machine 100 of FIG. 1 is stopped. Referring again to FIG. 7, and continuing again with process 400, the profile of the polished optic or other workpiece is measured in step 450, according to methods previously described. A decision is made at step 455, wherein if the optic 10 is acceptable against specifications, it proceeds through a step 490 of final measurement/quality control, and/or packaging, and shipping.

[0116] If such optic is not acceptable against specifications, steps are taken to prepare for another polishing cycle 440. Such steps include step 460, reprogramming of the CNC controller; optional step 470 of setting up/installing/and/or changing to a new polishing tool; and step 480, calculation of a new deterministic path for the next polishing cycle 440. The second polishing cycle then proceeds as previously described, and further iterations of steps 450-480 and 440 occur until the optic is polished to a condition that is acceptable against specifications, at which time step 490 is performed.

[0117] Included within the scope of the present invention is another embodiment of a polishing tool for the polishing of concave surfaces. FIG. 8A is a cross-sectional view of such a preferred polishing tool. Referring to FIG. 8A, polishing tool 300 comprises a mandrel 302 within which is disposed a groove 303 around the outer periphery of a flange 305 formed at one end of mandrel 302. Tool 300 further comprises a dome-shaped bladder 304, having a lip 307 that is disposed in groove 303 of mandrel 302. Compression washer 306 is fitter over the shank 301 of mandrel 302 and disposed against lip 305 of bladder 304. Locking nut 308 is threadedly engaged with a corresponding threaded portion of shank 301, such that locking nut 308 compresses lip 305 of bladder 304 into groove 303 of mandrel 302, thereby sealing bladder 304 to mandrel 302. Bladder 304 sealed to flange 305 of mandrel 302 thus forms a cavity 316 therebetween. Suitable materials for bladder 304 are e.g., natural or synthetic rubber, silicone, or polyurethane.

[0118] Numerous other embodiments of tool 300 are possible, wherein bladder 304 is formed such that bladder 304 fully encloses the outer surface 309 of the distal end of mandrel 302. In one embodiment, bladder 304 is conical, as indicated by dotted lines 311. In other embodiments, bladder 304 may have a parabolic shape, a hyperbolic shape, or combinations and transitions between hemispherical, conical (linear), hyperbolic, and parabolic surfaces at different radial zones along the surface of bladder 304. Thus bladder 304 may have a precisely hemispherical shape, a precisely conical shape, or a generally curved or domed shape formed by some combination of these various surface definitions. It will be apparent that even in the instance of a conically shaped bladder 304, that such bladder will likely be formed with a slight radius at the apex of such cone.

[0119] Mandrel 302 is further provided with an axial bore 312 disposed from the outer end 324 of shank 301 through the center of flange 305, such that the outer end 324 of mandrel 302 is in communication with cavity 316. Polishing tool 300 further comprises an inflation device 320 such as e.g., a check valve, or a tire valve stem, for providing a means to pressurize cavity 316 and maintain pressure therein, as previously described for tool 200 of FIG. 2A. Cavity 316 may be pressurized with any suitable fluid such as the liquids or gases previously described in this specification. In a further embodiment, axial bore 312 is connected during the polishing process to an adjustable pressure source, so that the pressure within cavity 316 may be varied in real time during the polishing operation, as described previously in this specification.

[0120] It will be apparent that in embodiments in which a relatively dense fluid, i.e. a liquid is used, and in which an elastic bladder is used, that the overall profile of the bladder, and therefore the spot size, can be varied as a function of polishing tool rotational speed. At relatively low rotational speed, a bladder with a substantially hemispherical shape will maintain such shape. As rotational speed is increased, the centrifugal force acting on the liquid contained in the bladder will deform the bladder into a flattened dome profile having a large radius of curvature near the center of the bladder, and a small radius of curvature near the lip 303 of the bladder. Such a feature can be used in the process of the present invention, wherein the polishing spot size is rendered adjustable as a function of rotational speed.

[0121] Referring again to FIG. 8A, polishing tool 300 further comprises a first ring or dome 332 of backing material disposed over the outer wall of bladder 304, and a second ring or dome 334 of polishing material adhered to dome 332, thereby forming a dual or composite ring or dome. In one embodiment, only a single ring or dome of material is used as the polishing medium, as described and shown for FIG. 4. Polishing tool is thus used in substantially the same manner as described for polishing tool 200 of FIG. 2A previously in this specification, with polishing tool 300 being the preferred tool for the polishing of concave surfaces. FIG. 8B is a side elevation view of the polishing tool of FIG. 8A, in the process of polishing a concave lens. Referring to FIG. 8B, it can be seen that the axis of rotation of polishing tool 300 is preferably disposed at an obtuse angle 50 with respect to the axis of rotation of concave lens 20, in order to achieve the desired contact between polishing surface 334 of toll 300 and concave surface 22 of lens 20.

[0122]FIG. 9 is a schematic representation of another preferred polishing apparatus for polishing concave spheres, aspheres, convex spheres, or other conformal shapes, such as lens 20 of FIG. 8B. Referring to FIG. 9, apparatus 150 is in one embodiment substantially similar to apparatus 100 of FIG. 1, with the main difference being provisions to contact the polishing tool with the concave surface of the workpiece. In order to accomplish this, the first preferred provision is the use of tool 300 of FIG. 8A, having a hemispherical, domed, or conical shape. A second preferred provision is in apparatus 150 wherein a B axis 152 directed into/out of the plane of FIG. 9 is provided, upon which polishing tool spindle 124 is mounted, and upon which polishing tool spindle 124 is bidirectionally rotatable, as indicated by arcuate arrow 154. Such a provision enables polishing tool 300 to be moved as indicated by arcuate arrow 156 into a position wherein the axis of rotation of polishing tool 300 is disposed at an obtuse angle 50 with respect to the axis of rotation of concave workpiece 20, as indicated in FIG. 8B. Such motion enables the polishing foil 334 of polishing tool 300 to contact the concave surface of a workpiece such as a concave lens or an asphere without having another portion of the polishing tool colliding with such workpiece.

[0123] It is to be understood that the machine 100 of FIG. 1, and the machine 150 of FIG. 9 that are provided to execute process 400 of FIG. 7, using tools 200 of FIG. 2A and tool 300 of FIG. 8A may have many different configurations. Axes types, spindle types, layout, size, provision of an automatic tool changer, and overall cost are just a few of the variables that could affect the desired design. While only show two specific possible machine configurations and specific possible tooling configurations are described in this specification and shown in FIGS. 1 and 9, it is to be further understood that many multi-axis CNC machine tools are known in the art, which can be suitably configured to use the polishing tools 200 and 300 and the process 400 of the present invention.

[0124] The overall computerized polishing process 400 using the apparatus 100 and polishing tool 200 of the present invention has many distinct advantages over prior art figure/polishing enhancement techniques, which are as follows:

[0125] 1. There are numerous options available with respect to size and shape of the bladder attached to the tool, such as a tire shape, hemisphere shape, domed shape, conical shapes, cylindrical shape, and the like. The shape of the bladder chosen depends on the part geometry and the desired process results. There are also options available in the choice of material composition and properties of the bladder. These options of size, shape, and material composition render the process of the present invention very versatile.

[0126] 2. Bladder inflation pressure is easily adjusted before the process begins and for many polishing process requirements, no pressure modification is required during the polishing process. In the event that it is desirable to adjust bladder pressure during the polishing process, a polishing tool and apparatus can be made to provide such additional process versatility.

[0127] 3. The method of inflating the bladder into the polishing foil makes replacement of the foil very simple, and typically no adhesive or mechanisms are required for attaching the foil to the bladder. Adhesive is only required to attach the foil to the PET ring.

[0128] 4. In using the polishing tools of the present invention, many types of materials may be wrapped around the bladder, thus allowing for the use of a wide variety of polishing foil media. Polishing foils may be made of e.g. polyurethanes, felts, synthetics, corks, leathers, and many other materials, depending on the desired polishing results. The foils may be impregnated with cerium, diamond, alumina, pitch, etc.

[0129] 5. The preferred method of placing the ring or foil upon the bladder also allows for modification of the shape of the foil or ring, i.e. the width, radius/contour or thickness thereof.

[0130] 6. In the preferred embodiment, the poly(ethylene terephthalate) ring that the foil may be attached to has not only great strength but also long lasting flexibility, which greatly extend the life of the polishing tool.

[0131] 7. The concept of the bladder tool allows for flexibility so that the polisher can conform to a variety of workpiece surface geometries and still maintain contact/polishing action upon such surfaces.

[0132] 8. In contrast to small spot polishing tools, the bladder polisher of the present invention will last and hold its shape much longer in operation. A polishing ring of material, and not just single spot develops the spot in the polishing tool and the process of the present invention, so the polishing surface area of the tool is greatly increased.

[0133] 9. The compression amount and spot size of the polishing tool can be easily adjusted by modifying the computer program to move the tool closer or further from the part in its path over such part.

[0134] 10. Because of the variety of shapes and types of materials that the various components of the polishing tool can be made from, the polishing process of the present invention has the flexibility to repair figure errors in a workpiece, and also achieve the highest surface quality requirements of such workpiece.

[0135] 11. In instances where the process may require one or more polishing tools to achieve the final results, this is easily accomplished with known machine tool automatic tool changing technology or multiple spindle technology, depending on the configuration of the particular machine.

[0136] 12. The powerful computer control algorithms provide the machine operator with a variety of flexible programs which, depending on desired results, can be easily modified and implemented, such as e.g., zigzag, circular, orbital, elliptical tool paths.

[0137] 13. Polishing of steels and other metallic components, especially those used in injection molds, and thin film coating dies can be done without the current technological limitations of prior art polishing processes.

[0138] In another preferred embodiment, the polishing tool further comprises actuation means to engage and/or extend and/or position and/or compress the inflatable bladder or other compliant part, and any polishing foil disposed thereupon, with respect to the part to be improved or polished. Such actuation means may comprise one or more linear actuating devices such as e.g., air operated or hydraulically operated cylinders.

[0139]FIG. 10 is a first perspective view of one such preferred polishing tool of the present invention comprising single cylinder actuation means to extend and/or position the inflatable bladder or other compliant part with respect to the part to be improved or polished. FIG. 11 is a side elevation view of the polishing tool of FIG. 10; FIG. 12 is a top view of the polishing tool of FIG. 10; and FIG. 13 is a second perspective view of the polishing tool of FIG. 10, taken from the plate side of the polishing tool.

[0140] Referring to FIGS. 11-13, polishing tool 500 comprises a base 502 to which various components are affixed. In the preferred embodiment, base 502 comprises a rigid plate of material such as steel, aluminum, or fiber reinforced polymer. Other base materials and or structures, such as a frame structure may be suitable, with the operative requirement being that the base is rigid enough to hold components attached thereto in sufficiently precise dimensional relationships so as to enable the overall precision polishing operation to be performed; and that the base is provided with provisions to enable the attachment of components thereto.

[0141] Toward the proximal end 504 of base 502, drive wheel 510 is operatively joined or attached to rotatable shaft 512, which is disposed in a housing 514 joined to base 502. Housing 514 is preferably joined to base 502 by threaded fasteners (not shown) engaged with tapped holes (not shown) therein, or by other suitable means. Rotatable shaft 512 is preferably disposed within means for enabling precise rotation, such as e.g., a bushing, or more preferably, bearings 516.

[0142] Tool 500 further comprises a polishing wheel 520, which is joined to linkage 530. Linkage 530 is operatively attached to actuating means 540, such that actuating means 540 actuates linkage 530, and thus moves polishing wheel 520, as indicated by bidirectional arrow 599. This motion of polishing wheel 520 serves to engage a polishing foil with a portion of the perimeters of polishing wheel 520 and drive wheel 510; such engagement will be described subsequently in this specification.

[0143] In the preferred embodiment depicted in FIGS. 10-13, actuating means 540 is a linear actuator, and in particular, actuating means 540 a pressure driven cylinder 542. Linkage 530 in this embodiment is a clevis 532 that is operatively joined to cylinder rod 544. Polishing wheel 520 is joined to clevis 532 by shoulder bolt 534, which passes through a hole in the center of wheel 520, and engages with nut 536. The position of wheel 520 is preferably maintained constant within clevis 532 by the use of spacing washers 535 and 537. In a further embodiment (not shown), polishing wheel 520 is provided with at least one bushing or bearing to minimize wear, friction and heat buildup, and to provide precise positional control in the event that polishing wheel is operated at high speeds.

[0144] Referring again to FIGS. 10-13, cylinder 542 is joined to base 502 at its proximal end by a shoulder bolt 547, which passes through bracket 543, and which is engaged with threaded hole 508 in base 502. Cylinder 542 is properly spaced out from base 502 by the use of jig bushing 546, through which bolt 547 also passes. Cylinder 542 is further joined to base 502 at its distal end by mounting nut 548, which is threadedly engaged with the housing 545 of cylinder 542, and also engaged with bracket 550. Bracket 550 is fastened to the distal end 506 of base 502 by threaded fasteners 552 and 554, which are engaged with tapped holes therein.

[0145] Cylinder 542 is thus rigidly secured to base 502, and thus in the operation of the tool 500 (to be described subsequently in this specification), cylinder 542 linearly actuates polishing wheel 520 as indicated by bidirectional arrow 599. To accomplish such actuation, cylinder 542 is operatively connected to a pressurized fluid supply at ports 556 and 558 in the housing 545 thereof, preferably provided through flexible hoses (not shown). Such fluid supply is selectable and switchable, i.e. fluid pressure may be applied at port 556 and fluid vacuum may be applied at port 558 to actuate wheel 520 away from distal end 506 of base 502 and toward the work piece 112 (see FIG. 18A), and fluid pressure may be applied at port 558 and fluid vacuum may be applied at port 556 to actuate wheel 520 toward distal end 506 of base 502 and away from the work piece 112. Such fluid cylinder actuating devices are well known. In addition, the pressurized fluid supply (not shown) may provide a pressurized gas such as air (i.e. cylinder 542 is an air cylinder), or pressurized fluid supply may provide a pressurized liquid such as a hydraulic oil (i.e. cylinder 542 is a hydraulic cylinder).

[0146] It will be apparent that actuating means 540 may comprise suitable linear actuators other than fluid pressure driven cylinders; many other linear actuators, such as rodless cylinders, stepper motors and other electromechanical actuators are well known and are to be considered within the scope of the present invention. Such linear actuators may be further provided with position sensing means, and/or position control means, and communication means for control thereof by an external process controller.

[0147] Tool 500 further comprises a polishing foil 680 (see FIG. 14), which is engaged with a portion of the perimeters of drive wheel 510 and polishing wheel 520. Polishing foil 680 thus has the function of a drive belt, rotationally coupling drive wheel 510 and polishing wheel 520 as indicated by arrows 598 and 597. (It will be apparent that the rotational direction could be the opposite of that depicted by arrows 598 and 597.) For the sake of simplicity of illustration, polishing foil 680 is not shown in FIGS. 10-13. Polishing foil 680 is shown in FIGS. 14-18B in the two-cylinder embodiment depicted therein. Polishing foil 680 is also shown in FIGS. 22A and 22B, for the purpose of illustrating the manner of engagement thereof with drive wheel 510 and polishing wheel 520, and for illustrating the preferred properties of polishing foil 680.

[0148]FIG. 22A and FIG. 22B are schematic representations of means for engaging a polishing foil of the polishing tool 500 of FIGS. 10-13. FIG. 22A depicts such engagement means in the retracted, or unengaged position, and FIG. 22B depicts such engagement means in the deployed, or engaged position. It is to be understood that the following description is also applicable to the polishing tool 600 of FIGS. 14 - 18B.

[0149] Referring to FIG. 22A, it can be seen that engagement means 540 comprising cylinder 542 is in the retracted position, as indicated by the short length of cylinder rod 544 that is visible therein. In the embodiment depicted in FIG. 22A and 22B, polishing foil 680 comprises an assembly similar to that described for ring assembly 230 of tool 200 of FIGS. 2A, 2B, 3, and 4, having a belt 682 of material and an abrasive ring 684.

[0150] Belt 682 is formed of an elastic material. In one embodiment, belt 682 consists essentially of a band of poly(ethylene terephthalate) having a thickness of between about 50 microns and about 2000 microns, and a width of between about 7 millimeters and about 125 millimeters. In another embodiments, belt 682 consists essentially of elastomers such as e.g., gum rubbers, polyurethane, silicone and the like. Many other belt materials may be suitable, with the operative requirement being that belt 682 have sufficient elasticity to stretch when rod 544 of cylinder 542 is deployed as shown in FIG. 22B, and that the outer surface of belt 682 is engageable with the inner surface of abrasive ring 684, either by friction, or by engagement features in the surfaces thereof, or by other means.

[0151] The abrasive ring 684 of foil 680 is made of a material of sufficient structural strength to withstand the high shear and tensile forces during polishing, and to resist degradation through exposure to the polishing/lubricating fluid, such as e.g. polyurethanes of various durometers; water resistant high strength cloth materials, and various types of felt, cork, and metal. Abrasive ring 684 further comprises abrasive particles embedded therein, or coated on the outer surface thereof, such as e.g. resin bonded diamond, alumina, and/or zirconium and the like. Abrasive ring 684 may have an inner surface having different types of backings, and/or patterns for engagement with belt 682.

[0152] Abrasive ring 684 preferably has a thickness of between about 1 millimeter and about 5 millimeters, and a width of between about 7 millimeters and about 125 millimeters. Additional operative requirements of abrasive ring 684 are that it have a greater circumference than belt 682, and that it is substantially inelastic, or significantly less elastic than belt 682, in order to enable proper engagement therewith.

[0153] The engagement of belt 682 with abrasive ring 684 is now described. Referring again to FIGS. 22A, belt 682 has been stretched at least slightly, and has been fitted such that belt 682 is engaged with portions of the perimeters of drive wheel 510 and polishing wheel 520. Belt 682 is thus under some tension, and when drive wheel 510 rotates as indicated by arrow 597, belt 682 is displaced as indicated by arrows 594, thereby resulting in rotation of polishing wheel 520 as indicated by arrow 598.

[0154] As can be seen in FIG. 22A, with rod 544 of cylinder 542 retracted, abrasive ring 684 is not engaged with belt 682, as indicated by gap 683 that is present between belt 682 and ring 684. Referring to FIG. 22B, when the rod 544 of cylinder 542 is deployed, polishing wheel 520 is displaced away from cylinder 542. Belt 682, being of an elastic material, stretches to the extent required to accommodate such displacement of wheel 520. Abrasive ring 684, however, being of a relatively inelastic material compared to belt 682, has not stretched, and has instead become engaged with belt 682 by friction, and/or by engagement features disposed on the contiguous surfaces thereof.

[0155] The rotation of drive wheel 520 in such circumstances thus results in the displacement of abrasive ring as indicated by arrows 593. Essentially, the actuation of cylinder 542 as indicated by arrow 599, in combination with the components attached thereto, acts as a clutch mechanism to engage and drive abrasive ring 684.

[0156] In another embodiment, polishing foil 680 may be formed as a unitary structure in a manner similar to ring 230 of FIG. 4 as described previously, but having both the required properties of a drive belt for engagement with wheels or pulleys, and an abrasive belt for polishing or more substantial surface removal, as well as having the requisite elastic properties as previously described. The applicant believes that the belt and ring structure is preferred, as such components are more easily and inexpensively provided, and such structure enables simple and rapid changeover between belts comprised of various abrasive media, either manually, or by automatic tool changing means.

[0157] In order to have good function as a drive belt engaged with wheels, polishing foil 680 may be provided with features known in drive belt art, such as grooves (not shown) on the inner surface thereof (mated with corresponding grooves in wheels 510 and 520); or teeth (not shown) on the inner surface thereof (mated with corresponding teeth in wheels 510 and 520 as is done with timing belts and pulleys); or knurling or other textures on the inner surface thereof. Drive wheel 520 may further be provided with rims extending radially outward from the edges thereof for improved belt retention, as is commonly done with drive pulleys.

[0158] Polishing foil 680 may vary in length from about 4 inches for tools having pulleys on the order of 0.25-0.5 inches in diameter to about 50 inches for tools having pulleys on the order of 8 inches in diameter. The rotational speed of drive wheel 510 is provided such that the surface speed of polishing foil 680 is between about 2 and about 1000 inches per second, depending upon the particular polishing application. Polishing foil 680 may further comprise fiber reinforcements disposed therein, and may comprise woven or cloth-like material, provided that sufficient elasticity is provided as described herein.

[0159] Referring once again to FIGS. 10-13, tool 500 further comprises a dowel pin 559 extending outwardly from and joined to base 502 by engagement with a threaded hole therein, or by an interference fit with a hole therein, or by other suitable means such as e.g. welding or adhesive. Dowel pin 559 is utilized to attach and/or stabilize tool 500 when it is engaged with drive means such as a CNC machine and used to polish an object. The details of such use will be described subsequently in this specification with reference to FIGS. 19-21. Tool 500 is preferably used in a multi-axis CNC apparatus for the polishing of objects; however, tool 500 may be engaged with a variety of more simple or more complex drive means, and used for many other surface polishing or surface abrasion applications. In one embodiment, tool 500 may simply be provided with an air motor or electric motor attached thereto as drive means, and placed in contact with the object to be worked.

[0160] Thus tool 500 may be fabricated at a variety of scales, depending upon the particular application, and in particular, the size, shape, and degree of finishing required of the part to be worked. The diameters of drive wheel 510 and polishing wheel 520 may vary from about 0.25 inches to about 8 inches. The scale of the other components, i.e. base 502, cylinder 542, and linkage 530 would be sized as required to operate drive wheel 510 and polishing wheel 520 and the foil 680 engaged therewith. For example, cylinder 542 may be provided with a bore of between about 0.1 inch and about three inches.

[0161] Although it appears in the embodiment shown in FIGS. 10- 13 that the diameters of drive wheel 510 and polishing wheel 520 are approximately equal, this is not an operating requirement. To the contrary, in some applications, it is advantageous to either increase the rotational speed of polishing wheel 520 or decrease the speed of polishing wheel 520 with respect to drive wheel 510, by providing polishing wheel 520 with a different diameter than drive wheel 510. The ratio of polishing wheel diameter to drive wheel diameter may vary from as much as about 1:10 to about 10:1, depending upon the application.

[0162] Polishing foil 680 may vary in width from about 0.25 to about 5 inches. The corresponding widths of drive wheel 510 and polishing wheel 520 thus vary in a similar manner in order to properly engage with and drive polishing foil 680.

[0163] The length of actuation stroke of means 540 (indicated by arrow 599) may vary from about 0.1 inch to about 3 inches, depending upon the scale of tool 500, and upon the degree of elasticity provided in polishing foil 680.

[0164] Referring again to FIGS. 10-13, and in the preferred embodiment depicted therein, polishing wheel 520 is preferably provided with a generally arcuate surface 521, and more preferably a spherical surface. Polishing foil 680, which is under tension from the action of actuation means 540, conforms to this surface 521 as it wraps around the perimeter of polishing wheel 520 during a polishing operation. This wrapping action results in better tracking of polishing foil 680 on polishing wheel 520. In addition, the radius of curvature and/or the curvature profile (spherical, elliptical, hyperbolic, etc.) of arcuate surface 521 partially determines the tool spot size during a polishing operation. Tool spot size has been described previously in this specification.

[0165] Referring to FIG. 12, in a further embodiment, wheel 520 is provided with a cavity 522 formed within the interior thereof, and a passageway 524 from the exterior of wheel 520 to cavity 522. Cavity 522 may thus be pressurized with various fluids during a polishing operation, as described previously in this specification with reference to tool 200 of FIGS. 2A and 2B, and tool 300 of FIGS. 8A and 8B. Passageway 524 may be further provided with an inflation device, such as inflation device 220 of FIG. 2A. In one embodiment, inflation device 220 is preferably a simple, inexpensive check valve. In a preferred embodiment, inflation device is a valve stem, or the inner workings thereof commonly used for the inflation of tubeless tires. Alternatively, inflation device may comprise a miniature check valve, such as one of many manufactured and sold by the Lee Company of Westbrook, Conn.

[0166] Polishing wheel 520 may be formed of suitable elastomers such as rubber, polyurethane, or silicone, or a harder or higher durometer polymer. The selection of material for polishing wheel 520 will depend upon whether or not polishing wheel 520 is provided with a cavity therein for pressurization, the extent to which such cavity may be pressurized and thus deformed, and the desired tool spot size during the polishing operation. These variables have been described in detail in this specification with regard to tool 200 of FIGS. 2A and 2B, and are also generally applicable to polishing wheel 520. In the preferred embodiment, polishing wheel 520 comprises a hub of solid material such as e.g. a plastic, ferrous, or non-ferrous metal (optionally including a bearing or bushing), and an exterior portion of elastomer (optionally including a pressurizable cavity therein), upon the perimeter of which is engaged the polishing foil. In the embodiment wherein polishing wheel does not include a pressurizable cavity therein, and is instead a solid elastomeric material, it is preferable that such elastomeric material be of a durometer between about 10 and about 90, with the particular durometer depending upon the polishing application.

[0167] In other embodiments, and depending upon the particular object to be polished or otherwise finished, polishing wheel may be formed with a plano (cylindrical) surface, or a convex surface. Polishing wheel 520 may also be formed with circumferential grooves on surface 521, or axial grooves (such as e.g. a timing pulley), and/or a texture such as knurling. These various surfaces may be employed to improve the tracking and/or traction between polishing wheel 520 and foil 680, thereby preventing slippage therebetween. These various surfaces may be further employed advantageously in that such surfaces may be used to cause high frequency vibrations of polishing wheel 520 and foil 680 against the part to be finished, thereby enhancing the polishing effect of tool 500.

[0168]FIG. 14 is a first perspective view of another preferred polishing tool of the present invention comprising twin cylinder actuation means to engage the polishing foil, and to extend and/or position the inflatable bladder or other compliant part, and the polishing foil disposed thereupon, with respect to the part to be improved or polished. FIG. 15 is a side elevation view of the polishing tool of FIG. 14; FIG. 16 is a top view of the polishing tool of FIG. 14; and FIG. 17 is a second perspective view of the polishing tool of FIG. 14, taken from the plate side of the polishing tool. It will be apparent that much of the structure of the embodiment depicted in FIGS. 14-17 is substantially the same as the embodiment depicted in FIGS. 10-13, with the main difference being the provision of twin cylinder actuation means in the embodiment of FIGS. 14-17. Accordingly, in the following description, only the twin cylinder actuation means will be described in detail, with the remaining structure and function of tool 600 of FIGS. 14-17 being as described for tool 500 of FIGS. 10- 13.

[0169] Referring to FIGS. 14-17, tool 600 comprises base 602, drive wheel 610 joined to shaft 612, polishing wheel 620, dowel pin 659, and polishing foil 680. Tool 600 further comprises actuation means 640, which further preferably comprises a first linear actuator and a second linear actuator. The first linear actuator is preferably a cylinder 642, and the second linear actuator is preferably a cylinder 662. First cylinder 642 is operatively connected to polishing wheel 620 by clevis 632, and thus provides linear actuation of polishing wheel as indicated by bidirectional arrow 699, in a manner similar to that described previously for tool 500 of FIGS. 10-13.

[0170] Second cylinder 662 is joined at the proximal end thereof by shoulder bolt 667, which passes through bracket 663 and spacer 666, and which is threadedly engaged with a tapped hole in base 602. Second cylinder 662 also provides linear actuation of rod 664 and clevis 633 inwardly and outwardly from cylinder body 665 as indicated by bidirectional arrow 696.

[0171] Since cylinder 662 is rotatable about shoulder bolt 667, this linear actuation of clevis 633 results in motion of the distal end of cylinder 642, and clevis 632 and polishing wheel 620 along a generally arcuate path as indicated by bidirectional arrow 695. This arcuate motion enables polishing wheel 620 and polishing foil 680 to be more effectively engaged with and compressed against the object to be polished, as will be subsequently explained with reference to FIGS. 18A and 18B.

[0172] Referring again to FIGS. 14-17, clevis 633 is joined to cylinder rod 664 and also to lock plate 670 by shoulder bolt 672. Lock plate 670 is also joined to the body 645 of cylinder 642, and lock plate is movably joined to base 602 by shoulder bolt 674, which passes through slotted opening 676 in lock plate 670. Referring to FIGS. 15 A and 15B in particular, FIG. 15A depicts the position of polishing wheel 620 with cylinder 662 fully retracted. FIG. 15B depicts the position of polishing wheel 620 with cylinder 662 fully deployed. It can be seen that lock plate 670 is displaced downwardly and outwardly resulting from the freedom of motion along slot 676, resulting in the arcuate motion of polishing wheel 620 and foil 680 as indicated by arcuate arrow 695. It will be apparent that many other combinations of a second linear actuator joined to a first linear actuator by a movable bracket, hinge, or other means can provide a suitable arcuate motion of polishing wheel 620, and thus all such combinations of linear actuators are comprehended within the scope of the present invention.

[0173] It is also noted that in the embodiment of tool 600 depicted in FIG. 17, although port hole 607 in plate 602 is depicted as being circular, port hole 607 may be oblong in the vertical direction, or of larger diameter. This variation in shape may be necessary because the arcuate motion of polishing wheel 620 as indicated by arrow 655 in FIG. 15B that results when cylinder 662 is deployed. This deployment and retraction of cylinder 662 causes the rod end of cylinder 642 to pivot up and down vertically as described previously. Since there is provided hydraulic fittings (not shown) connected to cylinder 642 through holes 607 and 609, and since the fittings and hose (not shown) connected to cylinder 662 through hole 607 has some significant amount of vertical travel, it may be necessary to enlarge or make oblong shaped hole 607, in order to provide operating clearance for such fittings and/or hose to move within hole 607 when cylinder 662 is deployed.

[0174] In a further embodiment, there is provided the tool of FIGS. 14-17, but with a simple pivotable link (not shown) in place of cylinder 642. In such an embodiment, there is preferably used a polishing foil 680 that is unitary in construction and that is elastic, such that polishing foil 680 is stretched over drive wheel 610 and polishing wheel 620, and engaged therewith. Thus first linear actuation means 640 comprising cylinder 642 is not provided. In the operation of such a tool, cylinder 642 provides the arcuate motion of polishing wheel 620, with wheel 620 pivoting along an arcuate path defined by the rigid link (not shown) provided in lieu of cylinder 642. (Substantially the same result could be obtained if cylinder 642 of tool 600 of FIG. 14 were locked in a fixed position, such that cylinder 642 would function as a rigid link.)

[0175]FIG. 18A is a cross-sectional elevation view of the polishing tool of FIG. 14, shown disengaged with a deeply concave object to be polished; and FIG. 18B is a cross-sectional elevation view of the polishing tool of FIG. 14, shown engaged from a deeply concave object to be polished. Referring to FIG. 18A, it can be seen that cylinder 662 is fully retracted as depicted in FIG. 15A, and that polishing wheel 620 and foil 680 are not in contact with object 112, there being a gap 114 between the inner surface 116 of object 112 and polishing foil 680. Referring to FIG. 18B, it can be seen that when cylinder 662 is subsequently fully deployed as depicted in FIG. 15B, polishing wheel 620 and foil 680 move along an arcuate path and make contact with object 112.

[0176] The fluid pressure applied to cylinder 642 and to cylinder 662 are among the parameters that determine the amount of force applied by polishing wheel 620 and foil 680 to the object 112, and which thus determine the tool spot size. Other parameters that determine such force and tool spot size are as described previously in this specification for tool 200 of FIGS. 2A and 2B, and tool 300 of FIGS. 8A and 8B.

[0177] In addition to the polishing tools described herein, and in accordance with the present invention, there is provided an apparatus for polishing objects comprising a computer numerically controlled (CNC) machine in which is fitted one of the tools of the present invention as depicted in FIGS. 10-18A. Various embodiments of such apparatus are depicted in FIGS. 19, 20, and 21.

[0178]FIG. 19 is a perspective view of a first preferred polishing apparatus of the present invention comprising a polishing tool having actuation means to extend and/or position the inflatable bladder or other compliant part with respect to the part to be improved or polished. FIG. 20 is a perspective view of a second preferred polishing apparatus of the present invention comprising a polishing tool having actuation means to extend and/or position the inflatable bladder or other compliant part with respect to the part to be improved or polished. FIG. 21 is a perspective view of a third preferred polishing apparatus of the present invention comprising a polishing tool having actuation means to extend and/or position the inflatable bladder or other compliant part with respect to the part to be improved or polished.

[0179] Referring to FIGS. 19-21, each of the apparatus therein are described with respect to the orthogonal x axis 107, y axis 105, and z axis 121 depicted therein. CNC machine 1000 is similar to that depicted in polishing apparatus 100 of FIG. 1, comprising a base 102 that supports Y-axis linear slide 104, the motion of which is bi-directional along Y-axis 105 as indicated by arrow 999. Linear slide 106, the motion of which is bi-directional along X-axis 107 as indicated by arrow 998, is mounted upon Y-axis linear slide 104. These linear slides 104 and 106 are both computer numerically controlled (CNC) positioning devices, providing programmable motion in the X-Y plane.

[0180] CNC machine 1000 further comprises vertical slide 120 attached to polishing machine frame or plate 123, which is joined to base 102. The motion of vertical slide 120 is bi-directional along Z-axis 121 as indicated by arrow 997. CNC machine 1000 is preferably provided with rotary axis 151, which is mounted upon vertical slide 120, and which is rotatable around B axis 152 (parallel to Z-axis 121) as indicated by bidirectional arrow 154. Polishing tool spindle 124 is attached to rotary axis 151. CNC machine 1000 further comprises a rotatable chucking device 126 attached to the end of polishing tool spindle 124, in which the drive shaft 612 polishing tool 600 of the present invention is inserted and rotated. Polishing tool 600 is positionable in a variety of orientations, several of which are depicted in FIGS. 19-21, depending upon the particular object to be polished. Polishing tool 600 is further affixed by a linkage (not shown), which attaches to pin 659 and which is joined to spindle 124, thereby immobilizing base 602 and preventing overall rotation of tool 600 by spindle 124. Thus only the drive shaft 612 of tool 600 is rotatable by spindle 124, while the remainder of tool 600 is held in position relative to object 112 to be polished.

[0181] Referring now only to FIG. 19, and in the embodiment depicted therein, apparatus 1010 comprises CNC machine 1000 further comprised of a work piece spindle 108 mounted upon linear slide 106. The motion of spindle 108 is bidirectionally programmable along axis 109, which is parallel to X-axis 107. Thus spindle 108 is movable by computer control along axis 109, depending on the requirements or the polishing process. The motion of object 112 in the X-Y plane with respect to tool 600 is programmable, and is performed by slides 104 and 106.

[0182] Rotatable work piece chucking device 110 is attached to end of work piece spindle 108. The work piece 112 to be polished is engaged and held by chuck 110 and rotated by spindle 108 around the central rotary axis 109 thereof as indicated by arrow 996. This rotary motion of object 112 results in the surface motion thereof being orthogonal to the motion of the polishing foil 680 (see FIG. 14) of tool 600. In this manner, such orthogonal motion of the object surface with respect to the foil substantially eliminates any “grooving” effect in the object surface by the polishing foil.

[0183] Referring now only to FIG. 20, and in the embodiment depicted therein, apparatus 1020 comprises CNC machine 1000 further comprised of a work piece spindle 162 mounted upon linear slide 106. Apparatus 1020 is similar to apparatus 1010 of FIG. 19, with the differences being in the orientation of the object 112 and the use of various slides and spindles to provide the relative motion between tool 600 and object 112. Spindle 162 is a vertically disposed spindle, the central axis 169 of which is parallel to Z-axis 121. Rotatable work piece chucking device 164 is attached to end of work piece spindle 162. The work piece 112 to be polished is engaged and held by chuck 164 and rotated by spindle 162 around the central rotary axis 169 thereof as indicated by arrow 995.

[0184] The motion of spindle 162 is bidirectionally programmable along the X axis 107 and the Y axis 105, both of which are perpendicular to the central axis of rotation 169 of object 112. To provide motion of tool 600 toward and away from object 112 in the direction of Z axis 121, rotary axis 151 and spindle 124 are rotated 90 degrees clockwise from their respective positions in FIG. 19, and slide 120 is used to move tool 600 axially in the Z direction.

[0185] Referring now only to FIG. 21, and in the embodiment depicted therein, apparatus 1030 is substantially the same as apparatus 1020 depicted in FIG. 20 in terms of components. Apparatus 1030 differs in setup in the position of spindle 162 on slide 106, and in the extent of rotation of rotary axis 151 and spindle 124, such rotation being about 30 degrees clockwise from their respective positions in FIG. 19. In addition, spindle 162 is locked, thereby preventing rotation of object 114, since object 114 is not axisymmetric. In the embodiment depicted in FIG. 21, object 114 is an equilateral prism, which thus requires the rotation of rotary axis 151 and spindle 124 of about 30 degrees. During the polishing operation, prism 114 is moved in the X and Y directions by the motion of slides 106 and 104 respectively, thereby moving prism in the X-Y plane with respect to tool 600. Tool 600 is moved in the Z-direction by slide 120, thereby enabling the foil 680 (see FIG. 14) of tool 600 to traverse up and down the sloped face 1 15 of prism 114.

[0186] In a further embodiment, the CNC machine 1000 is programmed to articulate tool 600 over the surface 115 of object 114 in a more complex path in X-Y-Z space. For example, tool 600 may be generally advanced along a linear path, but with a circular motion sumperimposed on such linear path. Such a tool path is known in the art as a trichordal path. Alternatively, and as described previously for the embodiments of FIGS. 1-9, such tool paths may include arcuate, zigzag, sinusoidal, or other combinations of motion so as to enhance the removal rate of material from object 114, and to prevent the occurrence of any “grooving” effect in the object surface during the polishing thereof.

[0187] It will be apparent that many other apparatus configurations are possible in fitting the tools of the present invention to CNC machines to polish and/or grind and/or otherwise finish objects. Such CNC machines may have more or fewer linear and rotational actuators as required by the particular application.

[0188] It will be further apparent that the polishing methods described herein and depicted in FIGS. 5, 6, and 7 for the operation of apparatus 100 of FIG. 1 and apparatus 150 of FIG. 9, using tool 200 of FIG. 2A and tool 300 of FIG. 8A are readily adaptable to tool 500 of FIGS. 10-13 and tool 600 of FIGS. 14-17, when such tools are fitted to apparatus 1010, 1020, or 1030 of FIGS. 19-21 respectively. In general, such methods may in some embodiments only differ by the setups of the particular tools 500 and 600, and in the additional control required of the linear actuating means, such as the fluid pressure provided to cylinder 542 (see FIG. 10) or cylinders 642 and 662 (see FIG. 14).

[0189] It will be apparent that there are many other apparatus configurations comprising actuation means that can increase the separation distance between two wheels, thereby providing increased tension of a belt engaged therewith; or that can increase the belt path length therearound (such as by an idler pulley), thereby providing increased tensioon of a belt engaged therewith, and that such actuation means are considered within the scope of the present invention. It will be apparent that there are many other apparatus configurations comprising actuation means that can adjust the position of a first wheel engaged to a second wheel by a belt, either along an arcuate path or a linear path or a combination thereof, and that such actuation means are also considered within the scope of the present invention.

[0190] It is, therefore, apparent that there has been provided, in accordance with the present invention, a method and apparatus for correcting figure errors, and for polishing objects comprising a wide variety of materials and shapes including precision optical surfaces and injection mold inserts; and in particular, objects having deeply concave precision surfaces. While this invention has been described in conjunction with preferred embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. 

We claim:
 1. A polishing tool comprising a) a base for affixing objects thereto; b) a drive wheel joined to a rotatable shaft, said drive wheel having a perimeter, and said rotatable shaft disposed in a housing joined to said base; c) a rotatable polishing wheel having a perimeter; d) a polishing foil engagable with a portion of said perimeter of said drive wheel and engagable with a portion of said perimeter of said polishing wheel, and. e) a first actuating means for engaging said polishing foil with said portion of said perimeter of said drive wheel and with said portion of said perimeter of said polishing wheel.
 2. The polishing tool as recited in claim 1, wherein said first actuating means comprises a first linear actuator operatively attached to said polishing wheel.
 3. The polishing tool as recited in claim 2, wherein said first linear actuator is a pressure-driven cylinder.
 4. The polishing tool as recited in claim 3, wherein said pressure driven cylinder is an air operated cylinder.
 5. The polishing tool as recited in claim 3, wherein said pressure driven cylinder is a hydraulically operated cylinder.
 6. The polishing tool as recited in claim 2, wherein said polishing foil comprises a belt.
 7. The polishing tool as recited in claim 6, wherein said belt is an elastic belt.
 8. The polishing tool as recited in claim 7, wherein said foil of further comprises an abrasive ring.
 9. The polishing tool as recited in claim 6, wherein said foil is impregnated with abrasive particles selected from the group consisting of ceria, alumina, silica, diamond, and mixtures thereof.
 10. The polishing tool as recited in claim 6, wherein said belt is a flat belt.
 11. The polishing tool as recited in claim 6, wherein said belt is a toothed belt.
 12. The polishing tool as recited in claim 2, wherein said polishing foil is between about 0.25 and about 5 inches wide.
 13. The polishing tool as recited in claim 2, further comprising a second actuating means for positioning said polishing wheel and said polishing foil.
 14. The polishing tool as recited in claim 13, wherein said second actuating means comprises a second linear actuator.
 15. The polishing tool as recited in claim 14, wherein said second linear actuator is a pressure-driven cylinder.
 16. The polishing tool as recited in claim 15, wherein said pressure driven cylinder is an air operated cylinder.
 17. The polishing tool as recited in claim 15, wherein said pressure driven cylinder is a hydraulically operated cylinder.
 18. The polishing tool as recited in claim 14, wherein said second linear actuator moves said polishing wheel along an arcuate path.
 19. The polishing tool as recited in claim 1, wherein said polishing wheel has an exterior portion consisting essentially of an elastomer.
 20. The polishing tool as recited in claim 19, wherein said elastomer is of a durometer of between about 10 and about
 90. 21. The polishing tool as recited in claim 1, wherein said polishing wheel has a cavity formed within the interior thereof.
 22. The polishing tool as recited in claim 21, wherein said polishing wheel further comprises a passageway into said cavity.
 23. The polishing tool as recited in claim 22, wherein said passageway has an inflation device disposed therein.
 24. The polishing tool as recited in claim 21, wherein said cavity contains a liquid.
 25. The polishing tool as recited in claim 21, wherein said cavity contains a gas.
 26. The polishing tool as recited in claim 1, wherein at least a portion of said polishing wheel has a spherical surface.
 27. The polishing tool as recited in claim 1, wherein said housing joined to said base has at least one bearing engaged with said rotatable shaft.
 28. The polishing tool as recited in claim 1, wherein said base comprises a substantially flat plate of rigid material.
 29. The polishing tool as recited in claim 1, further comprising a dowel pin disposed in said base.
 30. The polishing tool as recited in claim 1, wherein said drive wheel and said polishing wheel are between about 0.25 and about 8 inches in diameter.
 31. A polishing tool comprising a) a base for affixing objects thereto; b) a drive wheel joined to a rotatable shaft, said drive wheel having a perimeter, and said rotatable shaft disposed in a housing joined to said base; c) a rotatable polishing wheel having a perimeter; d) a polishing foil engaged with a portion of said perimeter of said drive wheel and engaged with a portion of said perimeter of said polishing wheel, and e) a first actuating means for for positioning said polishing wheel and said polishing foil.
 32. The polishing tool as recited in claim 31, wherein said first actuating means comprises a first linear actuator operatively attached to said polishing wheel.
 33. The polishing tool as recited in claim 32, wherein said first linear actuator is a pressure-driven cylinder.
 34. The polishing tool as recited in claim 32, wherein said first linear actuator moves said polishing wheel along an arcuate path.
 35. An apparatus for polishing objects comprising: a) a first linear slide movable along a first axis, disposed upon a base; b) a first rotatable spindle engaged with said first linear slide, said first rotatable spindle further comprising a first chuck, and said first rotatable spindle aligned with said first axis; c) a second linear slide movable along a second axis, engaged with said first linear slide, with said second axis disposed orthogonally to said first axis; d) a second rotatable spindle engaged with said second linear slide, said second rotatable spindle further comprising a second chuck; and e) a polishing tool engaged with said second chuck of said second rotatable spindle, said polishing tool comprising a base for affixing objects thereto; a drive wheel joined to a rotatable shaft, said drive wheel having a perimeter, and said rotatable shaft disposed in a housing joined to said base; a rotatable polishing wheel having a perimeter; a polishing foil engagable with a portion of said perimeter of said drive wheel and engagable with a portion of said perimeter of said polishing wheel, said polishing foil rotatably coupling said drive wheel with said polishing wheel; and a first actuating means for engaging said polishing foil with said portion of said perimeter of said drive wheel and with said portion of said perimeter of said polishing wheel.
 36. The apparatus as recited in claim 35, wherein said actuating means is a first linear actuator.
 37. The apparatus as recited in claim 36, wherein said first linear actuator is a pressure-driven cylinder.
 38. The apparatus as recited in claim 35, further comprising a second actuating means for positioning said polishing wheel and said polishing foil.
 39. The apparatus as recited in claim 38, wherein said second actuating means is a second linear actuator.
 40. The apparatus as recited in claim 39, wherein said second linear actuator is a pressure-driven cylinder.
 41. The apparatus as recited in claim 35, further comprising a third linear slide movable along a third axis, engaged with said first linear slide, and engaged with said second linear slide, with said third axis disposed orthogonally to said first axis and said second axis.
 42. The apparatus as recited in claim 41, further comprising a computer in control of said first linear slide, said second linear slide, said third linear slide, said first rotatable spindle, and said second rotatable spindle.
 43. The apparatus as recited in claim 35 further comprising a fluid delivery system comprised of a reservoir, a pump, and a fluid conduit directed at said foil of said polishing tool.
 44. A method of polishing a surface of an object using a machine tool apparatus comprising a polishing tool comprised of a base for affixing objects thereto; a drive wheel joined to a rotatable shaft, said drive wheel having a perimeter, and said rotatable shaft disposed in a housing joined to said base; a rotatable polishing wheel having a perimeter; a polishing foil engagable with a portion of said perimeter of said drive wheel and engagable with a portion of said perimeter of said polishing wheel, said polishing foil rotatably coupling said drive wheel with said polishing wheel; and a first actuating means for engaging said polishing foil with said portion of said perimeter of said drive wheel and with said portion of said perimeter of said polishing wheel; said method comprising the steps of: a) preparing said polishing tool for said polishing of objects; b) preparing and programming said machine tool for said polishing of objects; c) executing a first polishing cycle with said machine tool apparatus, wherein said polishing tool is in contact with said surface of said object; and d) measuring said surface of said object. 